1. Field of the Invention
This invention relates a high efficiency converter for ZVS{zero voltage switching}, particularly that having both advantages of traditional active clamp flyback circuit and asymmetric flyback circuit so as to act in ZVS for whole wide range of input voltage.
2. Description of the Prior Art
Recently we are under state of continual inevitable request of system specification augmentation such as multimedia system construction, acceleration of CPU to high speed, memory increase according to worldwide trend that notebook PC becomes day by day smaller, lighter, slimmer and pursuing high functionalization.
And as capacity for each resource of each system specification is increasing, though now AC adapter for notebook PC uses 45xcx9c50 watts, gradually need is rising up for making high capacity of 60 W, 75 W, 80 W or more, for making it a micro slip easy and simple of carrying and handling, and for high efficiency.
Particularly the reason to make AC adapter in high efficiency is that higher efficiency means lower internal electricity loss, which means lower internal heat generation so that miniaturization be feasible.
Accordingly soft switching is adopted to make AC adapter in high efficiency for the most typical type used in AC adapter so far, whence switch loss should be minimized by means of typically applying ZVS for the above soft switching.
Typical circuit realization methods for the above ZVS are symmetrical flyback circuit and active clamp flyback circuit, among which there occurs setback that input voltage should be doubled up by installing doubler circuit in case of the above asymmetric flyback circuit.
And there occurs disadvantage that drain-source voltage of FET used for switching element in the above active clamp flyback circuit is clamped to substantially high voltage adding the input voltage and the clamp capacitor voltage together.
Problem matter of traditional technique is considered hereunder with reference to appended drawings.
FIG. 1 is circuit diagram that shows active clamp flyback circuit layout in traditional technique, referring to which Figure the circuit is laid out by high side switch SWH and low side switch SWL making a closed circuit with input voltage Vin and each making a switching action that is opposite to each other according to output signal of external driver (not shown in Figure), a capacitor C connected in series between the above SWH and SWL, a transformer T that induces primary side voltage to secondary side according to switching action of the above SWH and SHL, and a rectifier that rectifies output voltage of secondary side of the above Transformer T.
Operation of traditional technique with configuration as above is explained hereunder.
At first comment, leakage energy is used for main switch""s ZVS which is realized as current Ic flows through parasitic diode of SWL in section between t1 and t3 and current Is flows through parasitic diode of SWH in section between t4 and t6.
Whence total action is as shown in FIG. 2 where high voltage is clamped by sum of input voltage Vin and capacitor C""s voltage Vc for the above SWH and SWL""s voltages VDSH, VDSL.
Typically used asymmetric flyback circuit with active clamp flyback circuit described above is laid out as in appended FIG. 3 where configurational difference from appended FIG. 1 is that capacitor C is placed between SWL and primary side coil of transformer T.
Thus simple difference in configuration makes to show a very large difference in its action state as shown in appended FIG. 4.
Namely in traditional technology as aforesaid while there is advantage in active clamp flyback circuit shown in FIG. 1 that here is no need of doubler necessary in asymmetric flyback circuit shown in appended FIG. 3, in contrast there is a different advantage in the above asymmetric flyback circuit that FET""s drain-source voltage used for switching element is stable because it is related only to input voltage differently from case of the above active clamp flyback circuit where the voltage is clamped in a considerably high voltage adding the input voltage and the clamp capacitor voltage together.
Accordingly (dis)advantage is so manifest for either side of the above active clamp flyback circuit and asymmetric flyback circuit that a designer should design taking advantage of only one side of the two cases but it contained problem matter that it has limit in satisfying users"" need which is strengthened step by step.
This invention is devised to solve the above problem matter whose purpose is to provide high efficiency converter for ZVS combining both side advantages of traditional active clamp flyback circuit and asymmetric flyback circuit to reduce drain-source voltage of switch (MOSFET), enhance adapter efficiency, and make the input voltage doubler circuit be not needed by means of making the converter to act in ZVS in wide range of whole input voltage.
According to main feature of this invention to achieve the above purpose, a high efficiency converter for ZVS is provided comprising high side switch (SWH) and low side switch (SWL) making a closed circuit with input voltage and each making a switching action that is opposite to each other according to output signal of external driver, first capacitor connected in series between the above SWH and SWL, a transformer that induces primary side voltage to secondary side according to switching action of the above SWH and SHL, and a rectifier that rectifies output voltage of secondary side of the above transformer while moreover the converter comprises a diode connected to the above first capacitor in parallel, first and second feedback diodes respectively connected to the above SWH and SWL in parallel, and second capacitor connected to primary coil of the above transformer in series.
Whence it is preferable according to additional feature of this invention that the above SWH and SWL are laid out containing MOSFET{metal-oxide semiconductor field-effect transistor}.